Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/54—Starch
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31971—Of carbohydrate
  • Y10T428/31975—Of cellulosic next to another carbohydrate

Definitions

• the present invention relates to an aqueous composition for the coating of paper and of cardboard.
• coating is meant the operation consisting on depositing on one or on both surfaces of a support sheet of paper or cardboard, a coating composition forming a coat; this coat confers on the treated sheet a particularly regular surface condition and hence adapted to receive well, fine printing, whilst improving the opaqueness and the appearance of paper (whiteness, smoothness, shine).
• a coating composition comprises at least two constituents, namely a pigment and a binder, also called adhesive.
• the first of these constituents, the pigment takes part as follows during the coating operation.
• the paper is constituted by fibres of variable dimensions which, in spite of the usual hot pressing operation, allow to subsist, on the one hand, at the surface cavities whose dimensions are of the order of 50 to 100 microns and, on the other hand, in the thickness of the paper, more or less wide channels, denoted by the term macro-capillaries.
• the surface is covered with a coat based on very fine pigments, the latter come to fill in the cavities thereby levelling the surface; the channels comprised by the layer thus applied are extremely fine: they are microcapillaries of a width of the order of 2 to 5 microns.
• the pigments of the ink which are coarser than the channels of the layer, remain at the surface whereas the support of the ink pigment which is constituted by oils and solvents is easily absorbed by the micro-capillaries, due to which the quality of the printing is improved.
• aqueous china clay or kaolin dispersion To constitute the pigment of the coating composition, recourse is generally had to an aqueous china clay or kaolin dispersion; it is also possible to use, either separately, or mostly in admixture with the clay, other pigments such as particularly calcium carbonate, titanium oxide, calcium sulfate, satin white (CaSO 4 +Al 2 O 3 ) or very fine talc.
• other pigments such as particularly calcium carbonate, titanium oxide, calcium sulfate, satin white (CaSO 4 +Al 2 O 3 ) or very fine talc.
• binder of the coating composition To constitute the binder of the coating composition, recourse is generally had to starches, proteins like casein or soya protein, or to synthetic products such as polyvinyl alcohol, polyvinyl acetate, acrylic products, styrene-butadiene.
• the composition can contain one only of these products, but often they are used in admixture.
• the amount of binder represents generally from 5 to 30% of the weight of pigment. This amount is chosen particularly according to the nature of pigment, according to the coating process used and according to the qualities sought for the paper or the cardboard. By way of example, it is indicated that it is convenient to employ more binder in the case of carbonate and satin white than in the case of clay, and in the case of finely divided fillers than in the case of coarse fillers.
• a coating composition comprises various additional agents among which may be mentioned foam reducers, preserving agents, dyes, dispersing agents or defloculating agents like tripolyphosphate, pyrophosphate or hexametaphosphate and the salts of polycarboxylic acids which retard particularly the sedimentation of the suspensions.
• the formulation of the coating composition varies according to the technique of application, the qualities of the support paper or of the properties sought, the latter being different according to the printing method (photogravure, typographic printing, offset, flexographic printing, silk screen printing) for which the coated papers are intended.
• starches used uptill now, alone or in admixture with proteins or the above mentioned synthetic substances to constitute the binder of the coating composition, are depolymerized starches, possibly modified in addition by etherification or esterification.
• the starches at present used in coating are depolymerised by acid or enzymatic hydrolysis, by oxidation, or by dextrinification, certain of these degradations (enzymatic or oxidising) being realisable directly on the user's premises.
• certain properties like bonding or "glaze” properties
• etherification or esterification acetylation, cationization, hydroxyethylenation or hydroxypropylenation, for example.
• the aqueous coating composition according to the invention is characterized by the fact that it comprises, besides the pigment:
• fluidizing agents selected from the group constituted by hydrogenated sugars comprising particularly sorbitol, mannitol, maltitol, xylitol, lactitol and hydrogenated starch hydrolysates, the proportion of fluidizing agent being from 0.40 to 20 parts by weight per 100 parts of pigment, and
• binder one or several undepolymerized starches, possibly modified by etherification, esterification or cross-linking.
• this composition comprises also one or several synthetic products of the group comprising particularly polyvinyl alcohol, polyvinyl acetate, acrylic products, styrene-butadiene, synthetic copolymers and/or one or several proteins selected particularly from the group comprising casein and soya proteins.
• starches which have not undergone a depolymerization treatment such as particularly acid or enzymatic hydrolysis, oxidizing degradation or dextrinification. They may be selected from among starches from any source and particularly from among corn starches, possibly hybrid, wheat starch and rice, potato flour, manioc starch. In addition, as already mentioned previously, these starches can have been etherified, esterified or cross-linked in order to modify certain of their properties like, for example, their stability in solution.
• a depolymerization treatment such as particularly acid or enzymatic hydrolysis, oxidizing degradation or dextrinification. They may be selected from among starches from any source and particularly from among corn starches, possibly hybrid, wheat starch and rice, potato flour, manioc starch.
• these starches can have been etherified, esterified or cross-linked in order to modify certain of their properties like, for example, their stability in solution.
• the presence of fluidizing agents enables the coating composition to be given a viscosity and a texture fully adapted to the coating of paper.
• undepolymerized starches enables all the previously described drawbacks to be overcome, which are associated with the use of degraded starches, and enables particularly higher binding power to be obtained, a better strength of the layer, a better water retention and a better homogeneity of the surface.
• a given pigment is essentially characterized, not only by its chemical composition, but also by the size and the disposition of its constituent particles.
• the description of the behaviour of the particles in the cluster is also important: number of particles, mobility or lack of mobility, breakage strength or resistance to rearrangement of the cluster and surface condition of the cluster.
• the constituent particles of the cluster can be coupled to one another by chemical bonds at the contact points, giving the clusters a strength almost equal to that of individual particles of the same size; they can also be rather weakly bound to one another as if they were attracted by magnetic or gravitational forces (Van de Waals force), these particular arrangements being “disturbable” or “breakable” by the application of a force.
• disagregation The dislocation of the clusters of particles bound by chemical linkages at their contact points is denoted by the term "disagregation". After disagregation or separation of the particles, the bonds are not reformed, the disagregation process hence being irreversible.
• dispersing agents is hence an essential part of the dispersion process which renders the use of mechanical energy effective and which reduces the viscosity of the suspension of pigments.
• a coating composition comprises particles of pigments and a binder, in an aqueous solution forming a fluid medium, in which the pigment particles are suspended.
• the fluid medium does not comprise only the binder or adhesive but also all the other dissolved materials, in particular the fluidizing agents used according to the invention.
• Starch or casein although in colloidal solution, are in a sufficient state of solubility for them to be considered as a part of the fluid.
• the fluid medium acts as a lubricant between the particles and permit them to slide over one another much more easily than they could if they were dry.
• the process of coating paper or cardboard according to the invention is characterized by the fact that there is applied, on one or both surfaces of the paper and of the cardboard, the aqueous coating composition according to the invention.
• Any conventional devices and equipment such brush coating devices or spreaders, CHAMPION spreaders, air sheet spreaders or scrapers, multiple roller spreaders or engraved roller spreaders, BILL-BLADE type spreaders and the like may be used for this application.
• the process of preparing the aqueous coating composition according to the invention is characterized by the fact that there is prepared, on the one hand, an undepolymerized starch glue, on the other hand, a pigment dispersion, the mixing of the starch glue and the pigment dispersion is carried out, and an effective proportion of fluidizing agent selected from the group constituted by hydrogenated sugars comprising especially sorbitol, mannitol, maltitol, xylitol, lactitol and hydrogenated starch hydrolysates, is introduced, by the addition either to the water serving for the preparation of the starch glue and/or of the pigment dispersion, or to the starch glue, or to the pigment dispersion, or to the mixture of both of them or to the final coating preparation.
• fluidizing agent selected from the group constituted by hydrogenated sugars comprising especially sorbitol, mannitol, maltitol, xylitol, lactitol and hydrogenated starch hydrolysates
• the cooking of the undepolymerized starch may be effected by any suitable technique and particularly by cooking in a live steam injection apparatus.
• this cooking is effected by a passage of a suspension of undepolymerized starch into an apparatus of the "Jet Cooker" type, well known to starch manufacturers, in which the cooking of the starch is obtained by the introduction of steam at a pressure above the atmospheric pressure.
• the cooking of undepolymerized starch is done at a dry matter comprised between 5% and 30%, at a temperature above 120° C. and in a time generally greater than 20 seconds, due to which an undepolymerized starch glue is obtained which practically no longer contains highly inflated but nonbursted granules, which are responsible for the viscosity developments and for a lack in stability.
• sorbitol or hydrogenated starch hydrolystates obtained by the acid and/or enzymatic hydrolysis of any starches followed by hydrogenation.
• These hydrogenated starch hydrolysates are constituted principally and in variable proportions according to the method of hydrolysis applied by sorbitol, maltitol, isomaltitol and hydrogenated oligo- and polysaccharides.
• the proportion of fluidizing agent entering into the coating composition according to the invention is about 0.40% to 20% by weight, preferably from 0.50% to 15% by weight, and more preferably still from 0.50% to 7.5% by weight.
• the amounts of binders used in the coating compositions according to the invention are from 5 to 30% by weight with respect to the weight of the pigments.
• the proportion of undepolymerized starch present in the coating composition according to the invention is established, the percentages being expressed dry/dry, between 0.2 and 30% and, preferably, between 0.5 and 30% by weight to the weight of pigment.
• the coating compositions according to the invention of which the binder is constituted at least in part by undepolymerized starch may be formulated with very high contents of dry matter, of the order of 60 to 70%, whilst having a viscosity compatible with their use on existing coating machines and whilst not giving rise to difficulties, for example in the final operation of filtration of the coating composition, which operation consists of freeing the composition particularly from the agglomerates that it may contain.
• Another advantage inherent in the use of the coating compositions according to the invention resides in the better plasticisation of the layer, contributed by the presence in the compositions of hydrogenated sugars and more particularly sorbitol.
• the pigments used were natural calcium carbonate and kaolin, and the dispersing agent used is constituted by a polyacrylate, sold under the trade mark DISPEX N 40 by the ALLIED COLLOIDS Company.
• the first composition was prepared from starch depolymerized enzymatically.
• a suspension of corn starch was treated in a continuous enzymatic converter such as constructed according to French Pat. No. 1,391,011 and marketed by Applicant, the enzymatic conversion being effected for 30 minutes at 85° C. in the presence of 1.4 parts of ⁇ -amylase per 1000 parts of starch.
• the inhibition of the enzyme was effected in the apparatus by a heat flash to 140° C. for 90 seconds.
• the undepolymerized starch glue was prepared by passing native corn starch in a Jet-Cooker, at a temperature of 150° C. and for 3 minutes under a pressure of 5 bars.
• the viscosities of the two coating compositions were then measured at 30° C., the storage being effected with and without shaking.
• the water retention was measured on an inclined plane or ramp and filters of the conventional FANN type of the type used for studying drilling muds, at a pressure of 6.9 bars.
• the viscosity of the coating composition based on undepolymerized starch is very much higher than that of the composition based on an enzymatically depolymerized starch.
• the HERCULES viscosity very representative considering the shear applied, is thus practically double that obtained with depolymerized starch; such a viscosity renders practically unapplicable use of the corresponding composition for the coating of paper and cardboard.
• the filtration of the composition in order to free it from agglomerates possibly present is rendered extremely difficult.
• This example illustrates the effect of the addition of sorbitol as a function of the moment selected for this addition to a coating composition containing undepolymerised starch as binder.
• the kaolin represents therefore 70% of the total filler and the calcium carbonate 30%.
• the dispersion of the pigments was carried out in 15 minutes at high speed on a CELLIER dispersor.
• composition according to the invention does not give rise to troublesome migration effects.
• the speed of the coating machine was 140 meters/minute, the temperature of the dryer 170° C. and the deposit (amount of composition per unit surface area) 12 g/m 2 .
• the IGT test is also appreciably improved.
• the ratio of incorporation of the various fluidizing agents tests was in all cases 1.29% dry/dry with respect to the pigments, the fluidizing agents having been added in the final preparation.
• the fluidizing agents tested were:
• the hydrogenated starch hydrolysate n o .1 corresponds to that marketed by the Applicant Company under the trademark NEOSORB 70/70®; it has the following composition, the percentages being expressed on dry matter:
• the hydrogenated starch hydrolysate n o obtained by hydrogenation of a starch hydrolysate of D.E. equal to 33, had the following composition:

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Citations (8)

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• 1982
  • 1982-10-12 FR FR8217085A patent/FR2540153B1/fr not_active Expired
• 1983
  • 1983-10-12 DE DE8383401993T patent/DE3370499D1/de not_active Expired
  • 1983-10-12 AT AT83401993T patent/ATE26138T1/de not_active IP Right Cessation
  • 1983-10-12 EP EP83401993A patent/EP0106763B1/fr not_active Expired
  • 1983-10-12 US US06/541,236 patent/US4600439A/en not_active Expired - Lifetime
  • 1983-10-12 CA CA000438870A patent/CA1218480A/fr not_active Expired

Patent Citations (9)

Non-Patent Citations (6)

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